I love him as Simon Brenner on ER. He started off as kind of an ass and additional to that, a stumbling block between the reunion of the much loved Neela & Ray. However he's come into his own and has become integral to the last season, finally winning resistant fans over. This is partly due to Simon's wonderful potrayal. Brenner is such a complex character but David has truly done a great job with him as the character has evolved in such a small amount of time. His scenes in Age of Innocence were heartbreakingly beautiful.
I'll definitely be keeping my eye on him in future projects. He's one to watch.